The invention concerns a hydrostatic steering arrangement with two control systems, each of which having a control unit with inner and outer rotary slide and a steering motor, one steering handwheel being common for both control units, and the control units being arranged in series in the axial direction of the rotary slides.
A steering arrangement of this kind is known from DE 196 22 731 C2.
A steering arrangement of this kind particularly serves the purpose of steering a vehicle. The two control systems are provided to make sure that on failure of one control system, the vehicle is still steerable by means of the other control system. As in the known case, the present invention also comprises a change-over valve, which changes over on failure of one control system, to make the other control system perform the steering. As both control units are operated by the same steering handwheel, the user should not feel a shift between the two control units. A failure of a control system should be displayed to the user.
However, in the known case, this cannot be realised to a sufficient degree. Each of the two control units namely has a cardan shaft, which is called a xe2x80x9cdog bonexe2x80x9d. This cardan shaft is required to make sure that the rotary movement of the measuring motor, in which a gear wheel is rotating and orbiting, can be transmitted to the outer rotary slide. The cardan shaft is connected with the gear wheel via a multi-spline connection. This connection always has a small tolerance. The connection from the steering handwheel to the second control unit has a correspondingly larger number of cardan shafts, which, in a similar way, are connected with heir counterparts by means of multi-spline connections, so that when operating the second control unit the operator experiences a much larger tolerance than when operating the first control unit. Accordingly, the steering behaviour of the steered vehicle in case of failure, that is on a failure of the first control system, is substantially more inaccurate. The operation behaviour of the vehicle is thus deteriorated, which should be avoided.
The invention is therefore based on the task of providing a steering, which works with a higher accuracy, also on failure of a control unit.
In a hydrostatic steering arrangement as mentioned in the introduction, this task is solved in that an inner rotary slide is provided, which is common for both control units.
The rotary slide is thus operated by the steering handwheel for both control units, and in both cases with exactly the same influence on the operation behaviour of the control unit in question. This is simply realised in that the inner rotary slide is extended in the axial direction in such a way that it can evolve the desired effect in both control units. In this connection, the inner rotary slide can be made in one piece. It can, however, also be made from two known rotary slides, which are unrotatably connected with each other. As the inner rotary slide is the only component having an immediate counter-effect on the user, this measure provides that the steering behaviour of the vehicle is always felt to be the same, independently of which of the two control units is effective.
Preferably, the outer rotary slide is also provided to be common for both control units. This makes it possible not only to let the immediate counter-effect on the operator be the same, both in the case of no failure and in the case of failure. Also the effects on the vehicle are then practially the same. The outer rotary slide is always rotated and following in the same way, independently of the question, which of the two control units is presently active. Additionally, this embodiment has the advantage that the inner and the outer rotary slides of each control unit are constantly moved, also when the second control unit is not active due to an unfailing operation of the first control unit. In this way it is prevented that any parts may get stuck. Thus, the second control unit is also always ready for operation.
Preferably, a measuring motor, which rotates the outer and the inner rotary slide of a control unit in relation to each other, has a toothed ring arranged eccentrically to the rotation axis of the rotary slide, in which toothed ring a gear wheel rotates and orbits, the gear wheel meshing so as to be rotary torque transmitting with the outer rotary slide. With this embodiment, the principle of a measuring motor, in which the gear wheel orbits and rotates in the toothed ring by way of the corresponding hydraulic pressures, can still be used. However, at the same time it may be ensured that the rotary slides can be driven without the insertion of eccentrically arranged driving parts. This simplifies the use of through rotary slides.
In this connection it is particularly preferred that the gear wheel has an inner toothing, which only meshes with an outer toothing of the outer slide on part of the circumference. This is a relatively simple way of realising a transmission of the rotary movement of the gear wheel to the outer slide without also transmitting the orbiting movement. The orbiting movement is simply absorbed in that in certain circumferential areas of the outer slide an adequate interstice is left open between gear wheel and slide. when the gear wheel orbits, the meshing between gear wheel and outer slide travels in the circumferential direction.
Preferably, each control unit has its own housing, and apart from a rotary transmission leadthrough on one front side of one housing, the housings are the same. Of course, one common housing for both control units can also be used. Using two separate housings, however, makes it possible to resort to housings, which are known and available from single control units. This simplifies both production and stocking. One of the housings merely has to be provided with a rotary transmission leadthrough, so that the shaft for the steering handwheel can be brought to meshing with the inner slide.
Preferably, the two housings are connected with each other through the insertion of a measuring motor section. In other words, the measuring motor section lies between the two housings and thus between the two control units. This gives a substantially symmetrical embodiment, which causes an additional improvement of the operating behaviour.
In this connection a preferred embodiment provides that the measuring motor section has a measuring motor for each control unit. Thus, the two control units are completely self-contained, so that, for example, also the failure of one measuring motor has no influence on the functioning of the steering arrangement.
In this connection a preferred embodiment may provide that in the measuring motor section at least one supply line is arranged to connect the two control units. The supply line can pass through the measuring motor section. Thus, a wiring from one control unit to the other on the outside of the housings can be saved.